There has been a long need in the field of drug delivery devices to have a drug released in the human body at the place where it is most therapeutically effective and to have said drug released in the body in a controlled manner over a long period of time.
There is art showing that poly(ortho ester)s and other polymers can be used as a matrix for drug release; however, there is no description in any of this art of the use of acid anhydrides as catalysts to promote the polymer erosion in a controlled fashion.
Also, the release of norethindrone from poly(ortho ester)s slabs has been described in the prior art. However, in this system a water-soluble salt such as sodium chloride and the like was incorporated into the polymer and the proposed mechanism for drug release in this case was osmotic imbibing of water, causing the matrix to swell and burst. The drug release was not controlled by polymer erosion but by a swelling process.